Comparación de dos métodos de digitalización y su influencia en la precisión obtenida en la determinación de parámetros topográficos

Se realizó una experiencia con el objetivo de establecer la precisión con que se obtienen algunos parámetros topográficos utilizando dos métodos de digitalización en la realización de un MDE: el convencional, con mesa digitalizadora (vectorial) y un método mixto que une la rasteri- zación producida por un escáner y la posterior vectorización con polilíneas generadas manualmente con un CAD. Se digitalizó un sector de una carta topográfica, estableciéndose la precisión con que se obtienen los parámetros topográficos más usados. Estos valores se compararon con los medidos directamente sobre la carta. El método de digitalización sobre tablero presentó un error posicional, de ± 16,4 m, el cual es superior al admisible. Las diferencias altimétricas se explicarían por la presencia de la banda épsilon en las curvas de nivel digitalizadas en mesa, inexistente en el método mixto, presentándose éste como una alternativa superadora para la digitalización de mapas

Niobium and rare earth minerals from the Virulundo carbonatite, Namibe, Angola

The Virulundo carbonatite in Angola, one of the biggest in the world, contains pyrochlore as an accessory mineral in all of the carbonatite units (calciocarbonatites, ferrocarbonatites, carbonatite breccias, trachytoids). The composition of the primary pyrochlore crystals is very close to fluornatrocalciopyrochlore in all these units. High-temperature hydrothermal processes caused the pseudomorphic replacement of the above crystals by a second generation of pyrochlore, characterized by lower F and Na contents. Low-temperature hydrothermal replacement of the above pyrochlores, associated with production of quartz-carbonates-fluorite veins, controled the development of a third generation of pyrochlore, characterized by high Sr contents. Finally, supergene processes produced the development of a secondary paragenesis in the carbonatite, consisting in late carbonates, goethite, hollandite and REE minerals (mainly synchysite-(Ce), britholite-(Ce), britholite-(La), cerite-(Ce)). Separation of Ce from the other REE was allowed by oxidizing conditions. Therefore, Ce4+ was also incorporated into a late generation of pyrochlore, which is also strongly enriched in Ba and strongly depleted in Ca and N

SALL1 modulates CBX4 stability, nuclear bodies and regulation of target genes

International audienc

Assessing the global prevalence of wild birds in trade

Publication status: PublishedAbstractTrade represents a significant threat to many wild species and is often clandestine and poorly monitored. Information on which species are most prevalent in trade and potentially threatened by it therefore remains fragmentary. We used 7 global data sets on birds in trade to identify species or groups of species at particular risk and assessed the extent to which they were congruent in terms of the species recorded in trade. We used the frequency with which species were recorded in the data sets as the basis for a trade prevalence score that was applied to all bird species globally. Literature searches and questionnaire surveys were used to develop a list of species known to be heavily traded to validate the trade prevalence score. The score was modeled to identify significant predictors of trade. Although the data sets sampled different parts of the broad trade spectrum, congruence among them was statistically strong in all comparisons. Furthermore, the frequency with which species were recorded within data sets was positively correlated with their occurrence across data sets, indicating that the trade prevalence score captured information on trade volume. The trade prevalence score discriminated well between species identified from semi‐independent assessments as heavily or unsustainably traded and all other species. Globally, 45.1% of all bird species and 36.7% of globally threatened bird species had trade prevalence scores ≥1. Species listed in Appendices I or II of CITES, species with large geographical distributions, and nonpasserines tended to have high trade prevalence scores. Speciose orders with high mean trade prevalence scores included Falconiformes, Psittaciformes, Accipitriformes, Anseriformes, Bucerotiformes, and Strigiformes. Despite their low mean prevalence score, Passeriformes accounted for the highest overall number of traded species of any order but had low representation in CITES appendices. Geographical hotspots where large numbers of traded species co‐occur differed among passerines (Southeast Asia and Eurasia) and nonpasserines (central South America, sub‐Saharan Africa, and India). This first attempt to quantify and map the relative prevalence in trade of all bird species globally can be used to identify species and groups of species that may be at particular risk of harm from trade and can inform conservation and policy interventions to reduce its adverse impacts.</jats:p